Field of the Invention
The present invention relates to a flexible tube for an exhaust pipe of an automobile, wherein a depression inner diameter in the center of a bellows is formed to be larger than a depression inner diameter at the both ends thereof such that a gap from an interlocking member increases so as to prevent the interference between the bellows and the interlocking member, thereby improving the driving noise due to the vibration and noise, and the depression portions of the both end portions are formed to be small so as to flexibly absorb the external force and displacement applied to the bellows, thereby improving the flexibility and durability of the bellows.
Description of the Related Art
In general, an exhaust pipe is connected to the engine of an automobile so as to discharge exhaust gas, wherein a flexible coupling is provided to the connection portion thereof such that the flexible coupling absorbs external force which is generated from the vibration of the engine and the vibration of the surface of a road so as to extend the lifespan of the exhaust pipe and improve the ride comfort.
The flexible coupling which is connected to the exhaust pipe of an automobile as above generally absorbs the tension, compression and bending displacement which are generated in response to the movement of an exhaust system from the engine vibration and the road surface vibration, wherein torsion displacement generated in every direction may follow according to the mounting conditions of the engine, the direction in which the displacement generates, and the design and shape of the entire exhaust pipe.
Therefore, a bellows made from a metal material is mainly used in order to improve the performances for maintaining airtightness and absorbing vibration and displacement, which are the core functions of the flexible coupling for an exhaust pipe of an automobile.
In addition, the flexible coupling is provided with an interlocking member as disclosed in EP 041089 A1, wherein the interlocking member simultaneously absorbs the deformation such as the inward compression, bending or the like of a bellows member which is made from a metal material in the shape of a cylinder with repetitive corrugations, controls the displacement within the range of elasticity limit of the bellows member, makes the flow of exhaust gas smooth as a guide tube, and protects the bellows member from the exhaust gas of high temperature.
Further, the bellow member is formed in a structure, in which the outside portion of the bellows member is surrounded by a braid member and, in this situation, the both ends of the bellows member and the braid member are compressed together with caps in the circumferential direction so as to be finished by spot-welding.
That is, one end is coupled to an engine side and the other side is coupled to an exhaust pipe side such that the exhaust gas passes through a center portion and the bellows member and the interlocking member absorb shocks, deformation or the like, which act between the engine and the exhaust pipe, through contraction and expansion.
The currently widely used bellows member have a disadvantage that the bellows member cannot sufficiently serve as a means for restraining the tension, compression and bending displacement caused by the vibration of an engine or the vibration of an exhaust system which is applied from the road surface while driving, since the outer diameter and the inner diameter of the bellows member are formed to be uniform so that the height of all protrusions is uniform or the height of just a first depression portion is lowered.
Therefore, in the flexible coupling, Korean Utility Model Registration Number 184089 discloses a flexible coupling for an automobile exhaust pipe as a means for extending the lifespan of a bellows and transmitting and dispersing the vibration of an engine and the vibration and stress generated during driving.
According to this flexible coupling for an automobile exhaust pipe, as shown in FIG. 6, the heights H1-H4 of protrusions gradually increase from a first protrusion at an end portion 11 side of a bellows member 10 to the other side and the inner diameter of the depression portion is formed to gradually decrease from a first depression portion to the other side at a uniform angle such that the flexible coupling absorbs displacement with respect to the axial direction or the bending direction of the braid member 10 and then is restored when the external force is removed.
Further, the depression portion minimum inner diameter Dr of the bellows member 10 is formed to be equal to or larger than the inner diameter Dt of the end portions 11.
However, the bellows member as described above has disadvantages that manufacturing costs increase and manufacturing work thereof is complicated since the bellows member is made from a metal material with repetitively formed protrusions and depressions, wherein the height of the protrusions gradually increases towards a center portion in the inward direction such that the inner diameter of the depressions gradually decreases.
Furthermore, the minimum inner diameter of the center portion of the bellows member is smaller than the diameter of the both end portions thereof such that the flow of exhaust gas stays in the center portion at the time of the discharge of the exhaust gas, thereby degrading engine performances.
In particular, a sufficient gap is secured between the interlocking member and the bellows member so as to prevent damage to the bellows member due to the mutual interference in the vibration or the generation of noise resulted from the mutual interference. However, the forming of such a sufficient gap causes the decrease of the height of the protrusions of the bellows member such that the durability of the bellows member becomes decreased or the noise may be generated.
That is, the vibration applied to the flexible tube in the exhaust system of an automobile is even serious in the center portion rather than the both end portions. Therefore, a sufficient gap is secured between the interlocking member and the bellows member. However, the bellows member as described above has the center portion of which inner diameter is the same as that of the conventional bellows member. Therefore, the center portion at which the serious vibration is applied cannot prevent the interference between the interlocking member and the bellows member with respect to the vibration or the like.